Many investigators believe that an extra-ocular stimulus acts on the eye to influence the intraocular pressure (IOP). The objective of this study is to search for the stimulus responsible for the diurnal variation in IOP. Hourly IOP and other vegetative functions such as blood pressure, pulse rate, rectal temperature, and selected hormones and blood chemistries will be monitored simultaneously. The subjects will be at bedrest during the 24 hour test period. A Mackay-Marg tonometer will be used to measure hourly IOP, and 20 minute blood samples will be obtained via an indwelling i.v. catheter. EEG's will be monitored during the sleeping hours. Sleep-wake cycles will be shifted 180 degrees and the response of the IOP and the tested variables will be correlated. The relation of IOP to the induced changes in the physiological parameters will also be evaluated. In addition, the diurnal IOP will be measured on subjects with unilateral Horner's syndrome, Adie's syndrome and unilateral lesions of cranial nerves II, III, IV, V, VI and VII, with the neurologically intact eye as the control. The frequent measurement of IOP will facilitate an evaluation of the "episodic nature" of the IOP. The results will be processed and plotted using a Hewlett Packard 2100A computer. This study assumes that an understanding of the mechanisms involved in the 24 hour cyclic changes of IOP will considerably advance the knowledge of the disease complex, known as glaucoma, and provide a basis for a more rational therapeutic approach.